Synchronized blocking oscillator



Oct.. 15, 19461 L. E. `McrsoN, JR 2,409,577

SYNCHRONIZED BLOCKING OSCILLATOR Filed Dec. 3. 1943 BY WV ATTORNEYPatented Oct. 15, 1946 SYNCHRONIZED BLOCKING OSCILLATOR Leslie E.Matson, Jr., Merchantville, N. J., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application December 3, 1943, SerialNo. 512,681

Claims.

l This invention relates to oscillation generators, and moreparticularly to an oscillator which blocks itself automatically, and isprovided with means for control of the intervals during which itintermittently oscillates, and also for synchronization of the first ofa series of oscillation trains or pulses with a suitable externalsignal.

There are many uses for apparatus of the type to Which this inventionrelates. One requirement in some of the applications involved is thatthere shall be made available apparatus for producing a succession ofperiodically recurrent oscillation trains; that is, trains of equalduration and equally spaced apart in time. Another requirement is thatthe rst train in such a group shall be synchronized with the leadingedge of a square Wave impulse of relatively low frequency. Blockingoscillators are, therefore, capable of improvement in accordance withthe disclosure of this application so that each train of oscillationsshall consist of a uniform number of cycles (usually one cycle), and theinitiation of the first of a group of trains of oscillations is socontrolled as to be precisely synchronized with a particular phase ofthe applied rectangular wave.

It is an object of my invention to provide a blocking oscillator ofvnovel type wherein the periods of oscillation are controlled by anexternal source of rectangular Waves.

It is a further object to provide a blocking oscillator wherein theleading edge of a square wave and the trailing edge thereof shall serveto initiate and to stop respectively the generation of oscillations.

Still another object of my invention is to provide a blocking oscillatorhaving a pentode tube in which the cathode, first grid, and anode areincluded in the oscillatory circuit, the second grid being arranged tofunction as a screen and the third grid being used to initiate and tostop the oscillations in dependence upon the keying of an externallyderived control potential.

Another object of my invention is similar to that set forth in thepreceding paragraph but with the added feature that an auxiliary tube isprovided for varying the control potential applied to the third grid ofthe oscillator tube.

The forego-ing and other objects and advantages of my invention will bemade clear from the description to follow. This description isaccompanied by a drawing, the sole figure of which shows a preferredcircuit diagram of apparatus units which are combined for carrying outthe invention.

Referring to the drawing, I show therein a discharge tube I which ispreferably of the pentode type having a cathode 2, an anode 3, a controlgrid 4, a second grid 5, and a suppressor grid 6. The cathode 2 isgrounded and is Valso connected to the grid E through a resistor 1. Theinput circuit of the oscillator proper includes a grid leak resistor 8connecting grid 4 to ground. Feedback means are coupled to this circuitand include a transformer 9, the primary I6 of which is in the outputcircuit of the oscillator, while the secondary'V II is coupled to thegrid 4 across capacitor I2. Anode potential is supplied to the anode 3across the transformer primary I0, be-

ing delivered by a direct current source I3. This source also suppliesscreen grid potential to the grid 5 across resistor I4. The usualby-pass condenser I5 is provided, one terminal of which is connected tothe screen grid 5 while the other terminal is grounded. Any suitableutilization device may be coupled to the oscillator at the terminalslabelled output, Where one of these terminals is coupled to the anode 3across capacitor IE. The output may, however, be taken at any of severalother points.

If the suppressor grid 5 is maintained at cathode or ground potential,tube I generates intermittently blocked oscillations by virtue of afeedback circuit through transformer S, the oscillatory electrodes beingthe cathode, the anode, and the control grid, as is conventional. If,however, a negative potential is applied to the suppressor grid withrespect to the cathode 2, then the oscillations are stopped. In order tosupply this negative potential, an auxiliary control tube I'I isprovided. This tube may, if desired, be of the triode type having acathode I8, an anode I9, and a control grid 20. A cathode resistor 2l ishere shown, this element being preferably used to avoid tube saturation.

An independent direct current source applies a negative potential to thecathode I8 through resistor 2|, the positive terminal of this sourcebeing grounded. The input circuit for tube il includes a grid leakresistor 23 connected between the grid 2l] and the negative terminal ofthe source 22. Grid 20 is also arranged to be fed with controlpotentials across capacitor 24. These control potentials develop asuitable voltage drop across the resistor 23. Input terminals 25, one ofwhich is grounded, may be used for applying suitable control potentials.These potentials are preferably of the rectangular or square wave typein order that the leading and 3 trailing edges of the wave may besharply defined.

In the operation of my invention, it will be seen that the square waveinput constitutes a gate voltage which controls the space path impedancein the tube I'I. When this tube is blocked by a negative potential onthe grid 20, then the anode I9 stands at ground potential since there isno voltage drop across the resistor 'I under these conditions. When,however, tube I1 is rendered conductive, it draws current by virtue ofthe negative potential applied to its cathode I8 from the source 22. Thecurrent traversing resistor 'i developsl a voltage drop which thereuponrenders the suppressor grid 6 strongly negative. Hence, the tube I isbiased to cut-oil and the oscillations instantly cease.

In this description of operation it should be emphasized that in usualpractice the oscillatory state exists in ,a blocking oscillator duringperiodic intervals which are very brief compared with the intervalsduring which the oscillator is blocked. The ratio between oscillatingtimes and blocking times depends, of course, upon the circuit constants.A train of oscillations, as herein referred to, consists of the singleimpulse or the plurality of impulses produced prior to each blockingperiod. Commonly, the blocking state is reached so suddenly that only asingle cycle exists in each train. Under some circumstances, however,each train may comprise a plurality of cycles. The function of theexternally derived rectangular wave is to periodically terminate theblocking periods. Thus it is possible to control the starting time forthe first of a group of oscillatory trains in accordance with the steepwave front of a rectangular wave and to permit the oscillator to delivera succession of trains comprised in that group during the persistence ofa half cycle of said rectangular wave.

At the instant when a group of oscillation trains is again to beinitiated in tube I, the trailing edge of the rectangular wave input totube I'I blocks this tube so as to restore the ground potential to itsanode IQ. Thereupon the suppressor grid S in tube I is brought back toground potential and the generation of oscillations is resumed.

It will be noted that the degree of accuracy with which the oscillatorytrains are synchronized with respect to an external source ofrectangular waves depends upon the abruptness of transition betweenconductive and non-conductive states in the tube I'I. Hence by acarefully selected choice of circuit components, the control andsynchronizing of oscillatory trains can be made as precise as isdesired.

My invention is capable of modication in numerous ways without departingfrom the spirit and scope thereof. For example, it is not at allessential that the control potentials applied to the tube Il' shall beperiodic. In certain applications, it is required that they shall beaperiodic, but that they, nevertheless, shall be enabled to initiate andto block the oscillatory trains generated by tube I regardless of theirduration and of the duration of the blocking periods.

I claim:

1. In a device of the class described, an oscillation generatorcomprising a discharge tube having a cathode, an anode, and at least twogrids, resonant circuit means connected to the Vcathode, anode, and rstgrid for producing oscilla- 4 tions, and a keying circuit for at timesblocking said oscillations, said keying circuit comprising a seconddischarge tube having at least a cathode, an anode and a control grid,the anode whereof is directly connected to a grid of the oscillator tubeadjacent its anode, an input circuit connected between the cathode andcontrol grid of said second discharge tube, and an output circuit forthe second discharge tube including a direct current source the positiveterminal of which is maintained at the cathode potential of the iirstsaid tube, a xed resistor being interposed between said positiveterminal and the anode of the second discharge tube.

2. In combination two electron discharge tubes, each having a cathode,an anode, and one or more grids, input circuits and output circuitsindividual to each of said tubes, the input and output circuit of one ofsaid tubes being so intercoupled as to cause that tube to generateperiodic and discrete oscillatory trains, two sources of direct current,each individually constituting a means for supplying power to arespective one of said tubes, direct ground connections for the negativeterminal of the source which supplies power to the oscillator tube andfor the positive terminal of the source which supplies power to theother tube, a load impedance connected between ground and the anode ofsaid other tube, a direct connection between that anode and a grid inthe oscillator tube other than its oscillator grid, and means for socontrolling the space path impedance in said other tube that, whenconductive, it interrupts the periodicity of production of saidoscillatory trains.

3. Apparatus for alternately initiating and interrupting trains ofoscillations generated in a discharge tube which possesses oscillatoryand suppressor electrodes, said suppressor electrode being iixedlyconnected through an ohmic resistance to the cathode of said tube,comprising a second discharge tube in which the space path impedance isvaried by a rectangular wave input, this second tube having its anoderesistively con- 1 nected to the cathode of the rst said tube, means forequalizing the bias potential of said suppressor electrode at all timeswith the anode potential in said second discharge tube, and means forshifting said anode potential from that of the cathode in the first saidtube to a more negative potential whenever the oscillatory trains are tobe blocked.

4. A control circuit comprising a vacuum tube to be controlled, saidvacuum tube having an anode, a cathode, a control grid and at least oneother grid, an input circuit connected between the control grid andcathode, said cathode being connected to ground, an output circuitconnected between said anode and cathode, a resistor connected betweensaid "other grid and the grounded cathode, a controlling vacuum tubehaving a plate, a control grid and a cathode, a cathode return circuitincluding a source of operating potential connected between the cathodef of the controllingtube and ground, the plate of said controlling tubebeing connected to said other grid in the first mentioned tube and theplate circuit including said resistor, and means for rendering saidcontrolling tube alternately conductive and non-conductive thereby tonegativeiy bias said other grid of the tube to be controlled duringconductive periods of the controlling tube.

5. In combination, a blocking oscillator comprising a multi-griddischarge tube and means coupling its output to one of its grids forapplying feedback potentials thereto, a keying control device directlyconnected between the cathode of said tube and a grid adjacent itsanode, said device comprising a fixed impedance in the output circuit ofa discharge tube the conductive and non-conductive states of which arecontrolled by an external source of rectangular Waves, independentsources of direct current in the respective output circuits of saidtubes, and ground l0 connections for the cathode of the oscillator tube,the negative terminal of the source in the oscillator output circuit,and the positive terminal of the source in the output circuit of thetube in said keying control device, the negative terminal of the lastmentioned source and the cathode of the tube in said keying device beinginterconnected through a cathode resistor.

LESLIE E. MATSON, JR.

